The Health Benefits of Emodin, a Natural Anthraquinone Derived from Rhubarb

Emodin (6-methyl-1,3,8-trihydroxyanthraquinone) is a naturally occurring anthraquinone derivative found in roots and leaves of various plants, fungi and lichens. For a long time it has been used in traditional Chinese medicine as an active ingredient in herbs. Among other sources, it is isolated from the rhubarb Rheum palmatum or tuber fleece-flower Polygonam multiflorum. Emodin has a wide range of biological activities, including diuretic, antibacterial, antiulcer, anti-inflammatory, anticancer and antinociceptive. According to the most recent studies, emodin acts as an antimalarial and antiallergic agent, and can also reverse resistance to chemotherapy. In the present work the potential therapeutic role of emodin in treatment of inflammatory diseases, cancers and microbial infections is analysed

Anthra-compounds are anthracene derivatives that have three fused benzene rings and one or more hydroxyl groups, which can bind to sugar molecules. That is why, in nature, they are found in the form of anthraquinone glycosides, most commonly with glucose or rhamnose as the sugar component. They are solid substances, usually in the form of orange crystals. The activity of anthra-compounds depends on their chemical structures and are related to the presence of hydroxyl groups at C-1 and C-8 in the aromatic ring, the nature of a substituent at C-3 and the number of sugar residues. Anthra-compounds occur either in oxidized (anthraquinones) or reduced form (anthrones, anthranols), and also as dimers (dianthrones). Reduction of anthraquinones leads to unstable anthrahydro-quinones and oxyanthrones. Naturally occurring anthraquinones find application as natural dyes, e.g., alizarin (Figure 1). Moreover, they display a range of desired biological activities. For example, one of the natural anthraquinones. chrysophanol, acts as an anti-inflammatory  and anticancer  agent. Anthraquinone derivatives isolated from microbial cells, such as 1-O-methyl chrysopchanol, isolated from Amycolatopsis thermoflava SFMA-103, have antihyperglycemic and antitumor properties. Similarly, naphthoquinones (e.g., 7-methyl juglone) and their derivatives have been widely studied with respect to their biological activity .

The natural antra-quinones.

Anthraquinones isolated from roots and leaves of plants belonging to families Polygonaceae, Rhamnaceae, Rubiaceae, Fabaceae and Scrophulariaceae and from fungi and lichens show a wide range of therapeutic effects . They have antihyperlipidemic, cholesterol-lowering, antiseptic, anticancer , and antimicrobial  properties. They can also find application in the treatment of kidney diseases, such as renal interstitial fibrosis (RIF) , or liver dysfunction. Additionally, there is research into new methods of functionalization of anthraquinones, and into synthesis of co-polymeric nanostructures designed for photodynamic therapy .

Emodin can be found in the roots, leaves, bark and trunk of several plants, such as Senna alata (Cassia alata) , Rumex abyssinicus , Odontites serotina , Reynoutria japonica , Polygonum cuspidatum. The source of emodin in the human diet is rhubarb . The roots and rhizomes of R. palmatum contain about 2.31 mg/g of emodin. Furthermore, the ethanol and acetone extract are 5.32 mg/g and 8.04 mg/g, respectively .